81. Consider the following diagram, where atom X is sented by a square and atom Y is represented by a circle. + (a) Write the equation for the reaction represented by the diagram. (b) If each circle stands for a mole of Y and each square a mole of X, how many moles of X did one start with? How many moles of Y? (c) Using the same representation described in part (b), how many moles of product are formed? How many moles of X and Y are left unreacted?​